Transcranial Magnetic Stimulation (TMS) delivered to targets within the brain or other parts of the nervous system has the capability of modulating neural activity. TMS may be used to treat many diseases and conditions. For example, positive outcomes for treatment of depression refractory to drug treatment have been demonstrated with rTMS (repetitive Transcranial Magnetic Stimulation, Avery et al., 2005). rTMS works indirectly by stimulating the dorsolateral pre-frontal cortex superficially; this superficial stimulation is carried by nerve fibers to the deeper cingulate gyrus. The ability to reach deep targets is of particular interest, but practical deep-brain TMS requires stimulation at depth without over stimulating superficial tissues. More effective therapy of depression and treatment of a number of other conditions such as chronic pain, addiction, obesity, and obsessive compulsive disorder would be possible with focused brain stimulation at depth. Devices for providing deep brain stimulation with Transcranial Magnetic Stimulation are described in Schneider and Mishelevich, U.S. patent application Ser. No. 10/821,807 and Mishelevich and Schneider, U.S. patent application Ser. No. 11/429,504.
Both superficial (e.g., cortical) and deep brain stimulation would benefit from rapid and accurate modeling and display of Transcranial electromagnetic fields on brain regions including a target brain region. In particular, systems for modeling and displaying the cumulative effect of TMS from multiple magnets would be useful. Existing methods are typically directed at display of only single-magnet systems that are concerned only with superficial brain regions. Modeling and display of electromagnetic fields from TMS electromagnets capable of penetrating deeper brain regions poses significantly different issues.
Currently available methods for modeling converging magnetic fields (for example, Wagner et al, IEEE Trans. Biomed. Eng. 2004 September; 51(9):1586-98 and Davey et al., Clin. Neurophysiol. 2003 November; 114(11):2204-9) are computationally intensive, and employ expensive software, such that making simple estimations of physically overlapping magnetic-field strengths may not be practical. In order to facilitate rapid device design and TMS treatment planning, there is a need for improved means for displaying modeled magnetic-field intensity at depth to assess the impact of different configurations of electromagnets in space and time for research or treatment planning. This includes the shaping of the magnetic fields generated by electromagnets by influences such as other electromagnets and high-permeability magnetic regions.
Hurme et al., U.S. patent application Ser. No. 11/853,232 and International Patent Application PCT/EP2007/059589, describes a method for displaying a visualization surface representative of a portion of the brain at a given depth overlaid on a volumetric image of the brain, the TMS-coil induced electric field and the coil itself. This display only relates to superficial brain just below the cranium rather than targets at depth.